112 MEMOIRS OF THE CARNEGIE MUSEUM 



I have elsewhere called attention to the fact that the characins parallel most 

 other fishes. For this reason they were distributed by the earlier naturalists 

 among various families of fishes. Pcecilocharax, a small species about the Kaieteur, 

 looked so nearly like a Poeciliid that only careful scrutiny after my arrival at home 

 enabled me to place it where it belongs. (Plate XLIV.) Not only do they parallel 

 other species of fishes, but they parallel each other. Moenkhausia lepidurus ' ' mimics ' ' 

 Creatochanes caudomaculatus, which frequently lives with it. The young of Ano- 

 stomus anostomus (Plate XLI, fig. 1) so closely resemble the young of Leporinus 

 arcus (Plate XLII, fig. 2) that a most skilled ichthyologist pronounced them the same 

 when the snouts of the two specimens were covered. Some idea of the diversity in 

 this family may be gathered by glancing at the plates from Numbers XXXIII to 

 LXI. The most interesting discovery was probably Bivihranchia, a characin with 

 a protractile upper jaw (Plate XXXIII) and of nearly equal interest was the dis- 

 covery of the sexually dimorphic Pcecilocharax (Plate XLIV, figs. 1 and 2). 



Of more general interest was the finding of the young of the "Pacu" in the Wara- 

 puta Cataract and elsewhere. The breeding-place of this important food-fish was 

 not known, and it had been supposed that it bred on the overflowed land during 

 the rainy season. 



Sexual Dimorphism. 



Color differences are as common between the sexes of fishes in Guiana as else- 

 where, but it is not the intention to take up these. Red and yellow are frequently 

 present.*^ Usually if yellow and red are present in a species the red replaces in 

 the male the yellow of the female. 



The seeondar.y sexual differences of the Poeciliidce are varied and great. They 

 have often been described, but none of those hitherto described approaches the 

 modification in the male of Tomeurus. (Plate LXV, figs. 7 and 8.) The anal fin in 

 this species has been moved further forward and is more highly modified than in any 

 other member of the family. In Rivulus (Plate LXIII) the female has an ocellus 

 on the base of the upper caudal lobe. (See also Plates LXIV and LXV for other 

 instances of sexual differences in the Poeciliidce.) 



Great secondary sexual characters are also found in the "Pacu," Myleus, and 

 probably in all of the related species of Myloplus. The anal fin in the male is 

 bilobed (Plate LIX, fig. 5), the middle rays longer than those either just in front 

 or behind them. The anal of the female is falcate (Plate LIX, fig. 6). 



^ In Hyphessobrycon and Hemigrammus the red of the caudal frequently encroaches on the sides of 

 the body. The red markings are sometimes very abrupt, as in the caudal of Cichla ocellaris, and in the fins of 

 Chaheus 7>iacrolepidotus. 



